a) Field of the Invention
The present invention relates to a stopping apparatus and method for an oil pump.
b) Description of the Related Art
A shift control hydraulic circuit for an automatic transmission is included in a hydraulic actuator which works based on a hydraulic pressure derived from the oil pump driven by a motor. The oil pump that is used as a source of the hydraulic pressure for a transmission mechanism of the automatic transmission is suggested to be driven by the motor instead of an engine. In such a case, (a drive of) the motor is deactivated when the shift control hydraulic circuit (or, the hydraulic actuator) is deactivated by turning an ignition switch off. At this time, the hydraulic pressure which remains, in a compressed fashion, within a controlling valve or the transmission mechanism that constitutes the shift control hydraulic circuit (hereinafter, also called a remaining pressure) flows toward the oil pump (i.e., flows in the opposite direction).
Such a backflow of an oil (or, a backflow of the remaining pressure) rotates the oil pump backward since the oil pump can rotate in any direction with the motor deactivated. Thereby, there is a problem that, for example, noise (or, abnormal sound) may be generated. In particular, this tendency (or, problem) is remarkable in a case where the oil pump is a vane pump which is favorably adopted for the automatic transmission.
With this fact taken into consideration, page 97 in a Japanese technical book “Mechanical engineering basic course 18 Hydraulic engineering (SI units edition) the second edition” published in April, 2003 by ASAKURA SHOTEN Co. Ltd. exemplifies a previously proposed stopping apparatus in which a countermeasure against this problem is taken as will be described below.
In a system including a transmission mechanism (namely, an automatic transmission), a controlling valve that performs a shift control for the transmission mechanism, an oil pump that supplies a hydraulic pressure to the controlling valve, and a motor that drives the oil pump, the controlling valve works based on the hydraulic pressure derived from the oil pump driven by the motor and sets a friction element inside the transmission mechanism to be selectively actuated (or, engaged) thereby, a required shift mode of the transmission mechanism is selected.
In such a system, a nonreturn (or, check) valve is interposed on a hydraulic route which establishes a connection between the controlling valve and the oil pump. Thereby, the nonreturn valve prevents an oil from (backward) flowing to the oil pump from the transmission mechanism or the controlling valve due to the remaining pressure within the transmission mechanism or the controlling valve. Hence, the oil pump does not rotate backward. A generation of the noise (or, the abnormal sound) due to such a backward rotation can be avoided.